As mobile device technology continues to develop and demand therefor continues to increase, demand for secondary batteries as energy sources is rapidly increasing. Accordingly, much research into secondary batteries which may satisfy various demands is underway.
Secondary batteries, which have superior electrical characteristics such as high capacity and high output, attract much interest as an energy source of mobile and wireless electronics such as cellular phones, digital cameras, PDA, laptops, etc., and power devices such as electric bicycles (E-bike), electric vehicles (EV), hybrid electric vehicles (HEV), etc.
However, in secondary batteries, decomposition of an active material, an electrolyte, etc. as battery components is caused in abnormal operation states such as overcharge, overdischarge, exposure to high temperature, short circuit, etc., and thus, heat and gas are generated. Accordingly, high temperature and high pressure are caused, and thus, decomposition is further accelerated, thereby leading to fire or explosion.
Further, generators or electrical connection elements, etc. of secondary batteries are slowly degraded due to continuous use, namely, continuous charge and discharge processes. For example, degradation of a generator leads to gas generation through decomposition of electrode materials, electrolyte, etc. Accordingly, a battery cell (can, pouch type case) slowly expands, more pressure is added to an expanded secondary battery in a limited case space, and risks such as fire and explosion may significantly increase under an abnormal operation condition.
Therefore, there is an urgent need for technology to resolve the problems of secondary batteries.